Polyethylene Fibers and Processes of Forming the Same

ABSTRACT

Fibers and methods of forming the fibers are described herein. The fibers generally include an ethylene based polymer exhibiting a molecular weight distribution of from about 2 to about 8.

FIELD

Embodiments of the present invention generally relate to fibers, and inparticular to fibers formed from polyethylene.

BACKGROUND

As reflected in the patent literature, fibers have generally been formedof propylene based polymers due to its low cost, processability andphysical properties. Attempts have been made to utilize ethylene basedpolymers to form such fibers. However, such attempts have not generallyresulted in adequate processability and physical properties. Therefore,it would be desirable to develop ethylene based polymers for use infiber production.

SUMMARY

Embodiments of the present invention include fibers and methods offorming the fibers.

The fibers generally include an ethylene based polymer exhibiting amolecular weight distribution of from about 2 to about 8.

The methods generally include providing an ethylene based polymer,wherein the ethylene based polymer exhibits a molecular weightdistribution of from about 2 to about 8, heating the ethylene basedpolymer to a molten state, extruding the ethylene based polymer to forma fiber and spinning the fiber at a desired spinning speed.

DETAILED DESCRIPTION Introduction and Definitions

A detailed description will now be provided. Each of the appended claimsdefines a separate invention, which for infringement purposes isrecognized as including equivalents to the various elements orlimitations specified in the claims. Depending on the context, allreferences below to the “invention” may in some cases refer to certainspecific embodiments only. In other cases it will be recognized thatreferences to the “invention” will refer to subject matter recited inone or more, but not necessarily all, of the claims. Each of theinventions will now be described in greater detail below, includingspecific embodiments, versions and examples, but the inventions are notlimited to these embodiments, versions or examples, which are includedto enable a person having ordinary skill in the art to make and use theinventions when the information in this patent is combined withavailable information and technology.

Various terms as used herein are shown below. To the extent a term usedin a claim is not defined below, it should be given the broadestdefinition persons in the pertinent art have given that term asreflected in printed publications and issued patents at the time offiling. Further, unless otherwise specified, all compounds describedherein may be substituted or unsubstituted and the listing of compoundsincludes derivatives thereof.

Further, various ranges and/or numerical limitations may be expresslystated below. It should be recognized that unless stated otherwise, it.is intended that endpoints are to be interchangeable. Further, anyranges include iterative ranges of like magnitude falling within theexpressly stated ranges or limitations.

Embodiments of the invention generally relate to fibers formed fromethylene based polymers.

Catalyst Systems

Catalyst systems useful for polymerizing olefin monomers include anycatalyst system known to one skilled in the art. For example, thecatalyst system may include metallocene catalyst systems, single sitecatalyst systems, Ziegler-Natta catalyst systems or combinationsthereof, for example. As is known in the art, the catalysts may beactivated for subsequent polymerization and may or may not be associatedwith a support material. A brief discussion of such catalyst systems isincluded below, but is in no way intended to limit the scope of theinvention to such catalysts.

For example, Ziegler-Natta catalyst systems are generally formed fromthe combination of a metal component (e.g., a catalyst) with one or moreadditional components, such as a catalyst support, a cocatalyst and/orone or more electron donors, for example.

A specific example of a Ziegler-Natta catalyst includes a metalcomponent generally represented by the formula:

MR^(A) _(x);

wherein M is a transition metal, R^(A) is a halogen, an alkoxy or ahydrocarboxyl group and x is the valence of the transition metal. Forexample, x may be from 1 to 4.

The transition metal may be selected from Groups IV through VIB (e.g.,titanium, vanadium or chromium), for example. R^(A) may be selected fromchlorine, bromine, carbonates, esters, or alkoxy groups in oneembodiment. Examples of catalyst components include TiCl₄, TiBr₄,Ti(OC₂H₅)₃Cl, Ti(OC₃H₇)₂Cl₂, Ti(OC₆H₁₃)₂Cl₂, Ti(OC₂H₅)₂Br₂ andTi(OC₁₂H₂₅)Cl₃, for example.

Those skilled in the art will recognize that a catalyst may be“activated” in some way before it is useful for promotingpolymerization. As discussed further below, activation may beaccomplished by contacting the catalyst with a Ziegler-Natta activator(Z-N activator), which is also referred to in some instances as a“cocatalyst.” Embodiments of such Z-N activators include organoaluminumcompounds, such as trimethyl aluminum (TMA), triethyl aluminum (TEAl)and triisobutyl aluminum (TIBAl), for example.

The Ziegler-Natta catalyst system may further include one or moreelectron donors, such as internal electron donors and/or externalelectron donors. Internal electron donors may be used to reduce theatactic form of the resulting polymer, thus decreasing the amount ofxylene solubles in the polymer. The internal electron donors may includeamines, amides, esters, ketones, nitriles, ethers, phosphines, diethers,succinates, phthalates, or dialkoxybenzenes, for example. (See, U.S.Pat. No. 5,945,366 and U.S. Pat. No. 6,399,837, which are incorporatedby reference herein.)

External electron donors may be used to further control the amount ofatactic polymer produced. The external electron donors may includemonofunctional or polyfunctional carboxylic acids, carboxylicanhydrides, carboxylic esters, ketones, ethers, alcohols, lactones,organophosphorus compounds and/or organosilicon compounds. In oneembodiment, the external donor may include diphenyldimethoxysilane(DPMS), cyclohexymethyldimethoxysilane (CDMS),diisopropyldimethoxysilane and/or dicyclopentyldimethoxysilane (CPDS),for example. The external donor may be the same or different from theinternal electron donor used.

The components of the Ziegler-Natta catalyst system (e.g., catalyst,activator and/or electron donors) may or may not be associated with asupport, either in combination with each other or separate from oneanother. The Z-N support materials may include a magnesium dihalide,such as magnesium dichloride or magnesium dibromide, or silica, forexample.

In one specific embodiment, the Ziegler-Natta catalyst is formed bycontacting a magnesium dialkoxide compound with sequentially strongerchlorinating and/or titanating agents. For example, the Ziegler-Nattacatalyst may include those described in U.S. Pat. No. 6,734,134 and U.S.Pat No. 6,174,971, which are incorporated by reference herein.

The Ziegler-Natta catalysts may be formed by methods generally includingcontacting an alkyl magnesium compound with an alcohol to form amagnesium dialkoxide compound. Such reaction may occur at a reactiontemperature ranging from room temperature to about 90° C. for a time ofup to about 10 hours, for example. The alcohol may be added to the alkylmagnesium compound in an equivalent of from about 0.5 to about 6 or fromabout 1 to about 3, for example.

The alkyl magnesium compound may be represented by the followingformula:

MgR¹R²;

wherein R¹ and R² are independently selected from C₁ to C₁₀ alkylgroups. Non-limiting illustrations of alkyl magnesium compounds includebutyl ethyl magnesium (BEM), diethyl magnesium, dipropyl magnesium anddibutyl magnesium, for example.

The alcohol may be represented by the formula:

R³OH;

wherein R³ is selected from C₂ to C₂₀ alkyl groups. Non-limitingillustrations of alcohols generally include butanol, isobutanol and2-ethylhexanol, for example.

The methods may then include contacting the magnesium dialkoxidecompound with a first agent to form reaction product “A”. Such reactionmay occur in the presence of an inert solvent. A variety of hydrocarbonscan be used as the inert solvent, but any hydrocarbon selected shouldremain in liquid form at all relevant reaction temperatures and theingredients used to form the supported catalyst composition should be atleast partially soluble in the hydrocarbon. Accordingly, the hydrocarbonis considered to be a solvent herein, even though in certain embodimentsthe ingredients are only partially soluble in the hydrocarbon.

Suitable hydrocarbon solvents include substituted and unsubstitutedaliphatic hydrocarbons and substituted and unsubstituted aromatichydrocarbons. For example, the inert solvent may include hexane,heptane, octane, decane, toluene, xylene, dichloromethane, chloroform,1-chlorobutane or combinations thereof, for example.

The reaction may further occur at a temperature of from about 0° C. toabout 100° C. or from about 20° C. to about 90° C. for a time of fromabout 0.2 hours to about 24 hours or from about 1 hour to about 4 hours,for example.

Non-limiting examples of the first agent are generally represented bythe following formula:

ClA(O_(x)R⁴)_(y);

wherein A is selected from titanium, silicon, aluminum, carbon, tin andgermanium, R⁴ is selected from C₁ to C₁₀ alkyls, such as methyl, ethyl,propyl and isopropyl, x is 0 or 1 and y is the valence of A minus 1.Non-limiting illustrations of first agents includechlorotitaniumtriisopropoxide ClTi(O^(i)Pr)₃ and ClSi(Me)₃, for example.

The methods may then include contacting reaction product “A” with asecond agent to form reaction product “B”. Such reaction may occur inthe presence of an inert solvent. The inert solvents may include any ofthose solvents previously discussed herein, for example. The reactionmay further occur at a temperature of from about 0° C. to about 100° C.or from about 20° C. to about 90° C. for a time of from about 0.2 hoursto about 36 hours or from about 1 hour to about 4 hours, for example.

The second agent may be added to reaction product “A” in an equivalentof from about 0.5 to about 5, or from about 1 to about 4 or from about1.5 to about 2.5, for example.

The second agent may be represented by the following formula:

TiCl₄/Ti(OR⁵)₄;

wherein R⁵ is selected from C₂ to C₂₀ alkyl groups. Non-limitingillustrations of second agents include blends of titanium chloride andtitanium alkoxides, such as TiCl₄/Ti(OBu)₄. The blends may have anequivalent of TiCl₄:Ti(OR⁵)₄ of from about 0.5 to about 6 or from about2 to about 3, for example.

The method may then include contacting reaction product “B” with a thirdagent to form reaction product “C”. Such reaction may occur in thepresence of an inert solvent. The inert solvents may include any ofthose solvents previously discussed herein, for example. The reactionmay further occur at room temperature, for example.

Non-limiting illustrations of third agents include metal halides. Themetal halides may include any metal halide known to one skilled in theart, such as titanium tetrachloride (TiCl₄), for example. The thirdagent may be added in a equivalent of from about 0.1 to about 5, or fromabout 0.25 to about 4 or from about 0.45 to about 2.5, for example.

The method may further include contacting reaction product “C” with afourth agent to form reaction product “D”. Such reaction may occur inthe presence of an inert solvent. The inert solvents may include any ofthose solvents previously discussed herein, for example. The reactionmay further occur at room temperature, for example.

The fourth agent may be added to the reaction product “C” in anequivalent of from about 0.1 to about 5, or from about 0.25 to about 4or from about 0.45 to about 2.0, for example.

Non-limiting illustrations of fourth agents include metal halides. Themetal halides may include any metal halide previously described herein.

The method may then include contacting reaction product “D” with a fifthagent to form the catalyst component. The fifth agent may be added tothe reaction product “D” in an equivalent of from about 0.1 to about 2or from 0.5 to about 1.2, for example.

Non-limiting illustrations of fifth agents include organoaluminumcompounds. The organoaluminum compounds may include aluminum alkylshaving the following formula:

AlR⁶ ₃;

wherein R⁶ is a C₁ to C₁₀ alkyl compound. Non-limiting illustrations ofthe aluminum alkyl compounds generally include trimethyl aluminum (TMA),triisobutyl aluminum (TIBAl), triethyl aluminum (TEAl), n-octyl aluminumand n-hexyl aluminum, for example.

Polymerization Processes

As indicated elsewhere herein, catalyst systems are used to formpolyolefin compositions, Once the catalyst system is prepared, asdescribed above and/or as known to one skilled in the art, a variety ofprocesses may be carried out using that composition. The equipment,process conditions, reactants, additives and other materials used inpolymerization processes will vary in a given process, depending on thedesired composition and properties of the polymer being formed. Suchprocesses may include solution phase, gas phase, slurry phase, bulkphase, high pressure processes or combinations thereof, for example.(See, U.S. Pat. No. 5,525,678; U.S. Pat. No. 6,420,580; U.S. Pat. No.6,380,328; U.S. Pat. No. 6,359,072; U.S. Pat. No. 6,346,586; U.S. Pat.No. 6,340,730; U.S. Pat. No. 6,339,134; U.S. Pat. No. 6,300,436; U.S.Pat. No. 6,274,684; U.S. Pat. No. 6,271,323; U.S. Pat. No. 6,248,845;U.S. Pat. No. 6,245,868; U.S. Pat. No. 6,245,705; U.S. Pat. No.6,242,545; U.S. Pat. No. 6,211,105; U.S. Pat. No. 6,207,606; U.S. Pat.No. 6,180,735 and U.S. Pat. No. 6,147,173, which are incorporated byreference herein.)

In certain embodiments, the processes described above generally includepolymerizing one or more olefin monomers to form polymers. The olefinmonomers may include C₂ to C₃₀ olefin monomers, or C₂ to C₁₂ olefinmonomers (e.g., ethylene, propylene, butene, pentene, methylpentene,hexene, octene and decene), for example. The monomers may includeolefinic unsaturated monomers, C₄ to C₁₈ diolefins, conjugated ornonconjugated dienes, polyenes, vinyl monomers and cyclic olefins, forexample. Non-limiting examples of other monomers may include norbornene,norbornadiene, isobutylene, isoprene, vinylbenzocyclobutane, sytrene,alkyl substituted styrene, ethylidene norbornene, dicyclopentadiene andcyclopentene, for example. The formed polymer may include homopolymers,copolymers or terpolymers, for example.

Examples of solution processes are described in U.S. Pat. No. 4,271,060,U.S. Pat. No. 5,001,205, U.S. Pat. No. 5,236,998 and U.S. Pat. No.5,589,555, which are incorporated by reference herein.

One example of a gas phase polymerization process includes a continuouscycle system, wherein a cycling gas stream (otherwise known as a recyclestream or fluidizing medium) is heated in a reactor by heat ofpolymerization. The heat is removed from the cycling gas stream inanother part of the cycle by a cooling system external to the reactor.The cycling gas stream containing one or more monomers may becontinuously cycled through a fluidized bed in the presence of acatalyst under reactive conditions. The cycling gas stream is generallywithdrawn from the fluidized bed and recycled back into the reactor.Simultaneously, polymer product may be withdrawn from the reactor andfresh monomer may be added to replace the polymerized monomer. Thereactor pressure in a gas phase process may vary from about 100 psig toabout 500 psig, or from about 200 psig to about 400 psig or from about250 psig to about 350 psig, for example. The reactor temperature in agas phase process may vary from about 30° C. to about 120° C., or fromabout 60° C. to about 115° C., or from about 70° C. to about 110° C. orfrom about 70° C. to about 95° C., for example. (See, for example, U.S.Pat. No. 4,543,399; U.S. Pat. No. 4,588,790; U.S. Pat. No. 5,028,670;U.S. Pat. No. 5,317,036; U.S. Pat. No. 5,352,749; U.S. Pat. No.5,405,922; U.S. Pat. No. 5,436,304; U.S. Pat. No. 5,456,471; U.S. Pat.No. 5,462,999; U.S. Pat. No. 5,616,661; U.S. Pat. No. 5,627,242; U.S.Pat. No. 5,665,818; U.S. Pat. No. 5,677,375 and U.S. Pat. No. 5,668,228,which are incorporated by reference herein.)

Slurry phase processes generally include forming a suspension of solid,particulate polymer in a liquid polymerization medium, to which monomersand optionally hydrogen, along with catalyst, are added. The suspension(which may include diluents) may be intermittently or continuouslyremoved from the reactor where the volatile components can be separatedfrom the polymer and recycled, optionally after a distillation, to thereactor. The liquefied diluent employed in the polymerization medium mayinclude a C₃ to C₇ alkane (e.g., hexane or isobutane), for example. Themedium employed is generally liquid under the conditions ofpolymerization and relatively inert. A bulk phase process is similar tothat of a slurry process with the exception that the liquid medium isalso the reactant (e.g., monomer) in a bulk phase process. However, aprocess may be a bulk process, a slurry process or a bulk slurryprocess, for example.

In a specific embodiment, a slurry process or a bulk process may becarried out continuously in one or more loop reactors. The catalyst, asslurry or as a dry free flowing powder, may be injected regularly to thereactor loop, which can itself be filled with circulating slurry ofgrowing polymer particles in a diluent, for example. Optionally,hydrogen (or other chain terminating agents, for example) may be addedto the process, such as for molecular weight control of the resultantpolymer. The loop reactor may be maintained at a pressure of from about27 bar to about 50 bar or from about 35 bar to about 45 bar and atemperature of from about 38° C. to about 121° C., for example. Reactionheat may be removed through the loop wall via any suitable method, suchas via a double jacketed pipe or heat exchanger, for example.

Alternatively, other types of polymerization processes may be used, suchas stirred reactors in series, parallel or combinations thereof, forexample. Upon removal from the reactor, the polymer may be passed to apolymer recovery system for further processing, such as addition ofadditives and/or extrusion, for example.

Polymer Product

The polymers (and blends thereof) formed via the processes describedherein may include, but are not limited to, linear low densitypolyethylene, elastomers, plastomers, high density polyethylenes, lowdensity polyethylenes, medium density polyethylenes, polypropylene andpolypropylene copolymers, for example.

Unless otherwise designated herein, all testing methods are the currentmethods at the time of filing.

The polymers may have a narrow molecular weight distribution(M_(w)/M_(n)). As used herein, the term “narrow molecular weightdistribution” refers to a polymer having a molecular weight distributionof from about 1.5 to about 8, or from about 2.0 to about 7.5 or fromabout 2.0 to about 7.0, for example.

In one or more embodiments, the polymers include ethylene basedpolymers. As used herein, the term “ethylene based” is usedinterchangeably with the terms “ethylene polymer” or “polyethylene” andrefers to a polymer having at least about 50 wt. %, or at least about 70wt. %, or at least about 75 wt. %, or at least about 80 wt. %, or atleast about 85 wt. % or at least about 90 wt. % polyethylene relative tothe total weight of polymer, for example.

The ethylene based polymers may have a density (as measured by ASTMD-792) of from about 0.86 g/cc to about 0.98 g/cc, or from about 0.88g/cc to about 0.965 g/cc, or from about 0.90 glee to about 0.965 glee orfrom about 0.925 g/cc to about 0.97 g/cc, for example.

The ethylene based polymers may have a melt index (MI₂) (as measured byASTM D-1238) of from about 0.01 dg/min to about 100 dg/min., or fromabout 0.01 dg/min. to about 25 dg/min., or from about 0.03 dg/min. toabout 15 dg/min. or from about 0.05 dg/min. to about 10 dg/min, forexample.

In one or more embodiments, the polymers include high densitypolyethylene. As used herein, the term “high density polyethylene”refers to ethylene based polymers having a density of from about 0.94g/cc to about 0.97 g/cc, for example.

In one or more embodiments, the ethylene based polymers are formed froma Ziegler-Natta catalyst.

In one or more embodiments, the ethylene based polymers are uni-modal.As used herein, the term “uni-modal” refers to a composition exhibitinga single molecular weight peak on a GPC plot.

In one or more embodiments, the ethylene based polymers aresubstantially linear.

Product Application

The polymers and blends thereof are useful in applications known to oneskilled in the art, such as forming operations (e.g., film, sheet, pipeand fiber extrusion and co-extrusion as well as blow molding, injectionmolding and rotary molding). Films include blown, oriented or cast filmsformed by extrusion or, co-extrusion or by lamination useful as shrinkfilm, cling film, stretch film, sealing films, oriented films, snackpackaging, heavy duty bags, grocery sacks, baked and frozen foodpackaging, medical packaging, industrial liners, and membranes, forexample, in food-contact and non-food contact application. Fibersinclude slit-films, monofilaments, melt spinning, solution spinning andmelt blown fiber operations for use in woven or non-woven form to makesacks, bags, rope; twine, carpet backing, carpet yarns, filters, diaperfabrics, medical garments and geotextiles, for example. Extrudedarticles include medical tubing, wire and cable coatings, sheets, suchas thermoformed sheets (including profiles and plastic corrugatedcardboard), geomembranes and pond liners, for example. Molded articlesinclude single and multi-layered constructions in the form of bottles,tanks, large hollow articles, rigid food containers and toys, forexample.

In particular, embodiments of the invention are useful for formingfibers including yarn and filaments. As used herein, the term “yarn”refers to a fiber formed from short fibers spun together continuously.The term “filament” refers to a continuous yarn produced directly byextruding from liquid polymer. In one or more embodiments, the articleincludes continuous fibers (e.g., filaments, which are referred toherein in specific embodiments as yarn). The yarn and filamentsdescribed herein may be used in applications known to one skilled in theart, such as carpet and textile applications.

One or more embodiments of the invention utilize the ethylene basedpolymers described above to form fibers. It has been observed that thefibers formed from embodiments of the invention generally result inimproved resiliency, lower luster and softer hand than thoseapplications utilizing propylene homopolymers.

In one specific embodiment of the invention, the fiber includes softtouch fibers. As used herein, the term “soft touch fiber” refers to thesoft touch feel of a fabric, generally referred to as hand. Generally,both finer denier and lower modulus contribute to the “softness” feel ofthe fibers and fabrics. It has been discovered that the ethylene basedpolymers described above may possess significantly improved fiberspinnability, thereby making it possible to produce finer denier fibersfrom ethylene based polymers. The soft touch fibers described herein maybe used in applications known to one skilled in the art, such asnon-woven applications including diapers. As used herein, the term“non-woven” is used to describe fabrics made through means other thanweaving or knitting.

In one or more embodiments, the fibers formed by the ethylene basedpolymers exhibit a tenacity at maximum load of from about 2.0 g/denierat a draw ratio of 3:1 to about 3.3 g/denier or from about 2.0 g/denierto about 3.0 g/denier, for example.

In one or more embodiments, the fibers exhibit a percent elongation atmaximum load of from about 250% at a draw ratio of 3:1 to about 325%, orfrom about 250% to about 300% or from about 250% to about 275%, forexample.

It has further been observed that the fibers formed by the ethylenebased polymers described herein also exhibit resistance to gammaradiation sterilization. See, U.S. Pat. No. 5,554,437 for a discussionof gamma radiation sterilization, which is incorporated by referenceherein.

EXAMPLES

Polymer “A” was formed from a Ziegler-Natta formed polyethylene having adensity of 0.962 g/cc and a molecular weight distribution of 6.0,commercially available from TOTAL PETROCHEMICALS USA, Inc. as 6450.

Polymer “B” was formed from a Ziegler-Natta formed polypropylene,commercially available from TOTAL PETROCHEMICALS USA, Inc. as 3762.

Monofilament fibers were formed from the polymer samples and analyzed.The fiber was spun at a forward spinning speed of 770 meters per minuteto produce a fully oriented fiber (FOY) using a two stage godet assemblyheated up at 80° C., 85° C. and 90° C. respectively. A maximum spinningspeed of 2000 m/min was measured. The FOY fiber was spun at 3:1, 5:1 anda maximum 7:1 draw ratio (DR).

The results are shown in Table 1 below.

TABLE 1 Polymer A Polymer B FOY # DDR 7:1 FOY # DDR 5:1 FOY # DDR 3:1FOY # DDR 5:1 (Max) FOY # DDR 3:1 (Max) Tenacity @ Max 2.5 +/− 0.1 3.3+/− 0.1 3.2 +/− 0.4 2.5 3.3 Load [g/denier] Tenacity @ 2.2 +/− 0.1 2.9+/− 0.1 2.9 +/− 0.3 2.2 2.9 Break [g/denier] Modulus @ 5% 8 +/− 1 13 +/−1  24 +/− 1  5 16 Elongation [g/denier] % Elongation @ 251 +/− 25  92+/− 14 36 +/− 23 199 102 Max Load [%] % Elongation @ 278 +/− 22  113 +/−9  54 +/− 26 218 111 Break [%] % Shrinkage at 19.9 15.7 8.2 6.4 7.4 100°C.

It was observed that the polyethylene fibers exhibited improvedprocessability and mechanical properties (e.g., a tenacity at maximumload that ranged from 2.2 g/denier at DR 3:1 to 3 g/denier at DR 7:1 anda percent elongation at maximum load that ranged from 278% at DR 3:1 to54% at DR 7:1). In fact, the polyethylene fibers had a tenacity andelongation at max comparable to polypropylene fiber that ranged from 2.5g/denier at DR 3:1 to 3.3 g/denier at DR 5:1 and a percent elongation atbreak that ranged from 251% at DR 3:1 to 92% at DR 5:1.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof and the scope thereof isdetermined by the claims that follow.

1-12. (canceled)
 13. A method of forming fiber comprising: providing anethylene based polymer exhibiting a molecular weight distribution offrom about 2 to about 8; heating the ethylene based polymer to a moltenstate; extruding the ethylene based polymer to form a fiber, wherein thefiber exhibits a tenacity at maximum load of from about 2.0 g/denier ata draw ratio of 3:1 to about 3.3 g/denier; and spinning the fiber at adesired spinning speed.
 14. The method of claim 13, wherein the ethylenebased polymer is formed by a Ziegler-Natta catalyst.
 15. The method ofclaim 14, wherein the Ziegler-Natta catalyst is formed by: contacting analkyl magnesium compound with an alcohol to form a magnesium dialkoxidecompound; contacting the magnesium dialkoxide compound with a pluralityof first agents to form reaction product “A”; contacting reactionproduct “A” with a second agent to form reaction product “B”, whereinthe second agent comprises a transition metal and a halogen; contactingreaction product “B” with a third agent to form reaction product “C”,wherein the third agent comprises a first metal halide and wherein thethird agent is a stronger halogenating agent than the second agent;optionally contacting reaction product “C” with a fourth agent to formreaction product “D”, wherein the fourth agent comprises a second metalhalide and wherein the fourth agent is a stronger halogenating agentthan the third agent; and contacting reaction product “D” with fifthagent to form a Ziegler-Natta catalyst component, wherein the fifthagent comprises an organoaluminum compound.
 16. The method of claim 13,wherein the ethylene based polymer is linear.
 17. The method of claim13, wherein the ethylene based polymer is uni-modal.
 18. The method ofclaim 13, wherein the ethylene based polymer exhibits a density of atleast about 0.94 g/cc.
 19. The method of claim 13, wherein the fiber isa soft touch fiber.
 20. The method of claim 13, wherein the fiber is afine denier monofilament that exhibits increased resistance to gammaradiation sterilization over a fiber formed from an identical processwith a Ziegler-Natta formed polypropylene homopolymer.
 21. The method ofclaim 13, wherein the ethylene based polymer comprises at least 50 wt. %polyethylene relative to a total weight of the ethylene based polymer.22. The method of claim 13, wherein the ethylene based polymer comprisesat least 70 wt. % polyethylene relative to a total weight of theethylene based polymer.
 23. The method of claim 13, wherein the ethylenebased polymer comprises at least 75 wt. % polyethylene relative to atotal weight of the ethylene based polymer.
 24. The method of claim 13,wherein the ethylene based polymer comprises at least 80 wt. %polyethylene relative to a total weight of the ethylene based polymer.25. The method of claim 13, wherein the ethylene based polymer comprisesat least 85 wt. % polyethylene relative to a total weight of theethylene based polymer.
 26. The method of claim 13, wherein the ethylenebased polymer comprises at least 90 wt. % polyethylene relative to atotal weight of the ethylene based polymer.